With every new iOS release, a jailbreak isn't far behind. Jailbreaking is the process of enabling read and write access to otherwise locked files on an iPhone, iPod touch or iPad.
There are many benefits of doing this, including the ability to install custom programs that aren't available on Apple's App Store and customise your device in ways that Apple doesn't currently allow, such as 3D transitions between home screens.
There are also disadvantages. As well as voiding your warranty, if you install apps from third-party app stores such as Cydia, there's a possibility it may contain malware. It's also possible your device's performance will suffer.
On September 19th 2012, Apple released iOS 6, reviewed, which added many new features worth upgrading for. Of course, updating a previously jailbroken device with a new iOS firmware removes the jailbreak, any custom software and tweaks, including the Cydia app store.
iPhone 5: jailbreak status
UPDATED: 4th Feb 2013. Developers, or hackers known as evad3rs, have found a flaw to exploit in the new Apple A6 processor. They've created an untethered jailbreak which will work on the iPhone 5, iPad mini and iPad 4th generation. It's called evasi0n.
Before using any jailbreaking tools, make sure you back up your iOS device using iTunes to make a full backup. Also, disable the passcode lock as it can cause problems.
Watch out for any websites that claim to have a working, untethered jailbreak for the iPhone 5, since it could be a phishing site looking to get hold of your personal details. Never hand out your email address or any other information in return for a promised download link.
One such website is offering a 'redpois0n' jailbreak, but it's a fake.
iPhone 4S: jailbreak status
As with the iPhone 5, iPhone 4S owners can use the evasi0n tool to jailbreak their phones running iOS 6.1.
iPhone 4: jailbreak status
Along with the other iDevices which use the A4 (or older) chip, namely the iPod touch 4th-gen and iPhone 3GS, an exploit was found which couldn't be fixed by software updates. This same exploit has been used to bring out a tethered jailbreak for these devices running iOS 6 (via OSXDaily).
Tethered vs untethered jailbreak
It's important to understand the difference between tethered and untethered jailbreaks. The former is something you don't really want, as you'll need to connect your phone to a computer in order to allow it to start after a reboot, or after the battery runs flat.
An untethered jailbreak means you can reboot the phone without consequence: everything will still work afterwards.
How to jailbreak iOS 6 using Redsn0w
Note: this is a tethered jailbreak and works with iPhone 4, iPhone 3GS, iPod touch 4th gen. The iPhone 5, iPhone 4S, iPad 2, iPad 3 and iPod touch 5th-gen are not supported. The original iPad isn't compatible with iOS 6, so isn't relevant here.
Step 1. Turn the device off, and connect it to your computer.
Step 2. Run Redsn0w (right-click and Run as administrator in Windows, or right-click and choose Open in OS X).
Step 3. Click the Jailbreak button, make sure Cydia is checked and follow the instructions to put your device in DFU mode.
Step 4. The jailbreak will install, but you'll need to tick the Autoboot option to boot your device after installation is complete.
Step 5. When your device reboots you should see a Cydia icon on one of your home screens, which you can use to install apps and other hacks.
Step 6. When you next need to reboot your device, connect it to your computer, run Redsn0w, click Extras and then the Just boot option. You'll need to put the device into DFU mode again.